Riesel may refer to: People Hans Riesel (1929–2014), Swedish mathematician who discovered a Mersenne prime Victor Riesel (1913–1995), American labor union journalist In Mathematics Riesel number, an odd natural number k for which the integers of the form k·2n−1 are all composite Riesel Sieve, a project to prove the smallest Riesel number Places Riesel, Texas